In modern agricultural seeding operations, a tractor typically pulls a plurality of furrow cutting and seeding units across a field to plant multiple rows of seeds simultaneously. Each row unit is designed to open a seed furrow, deposit seeds within the seed furrow, and close the seed furrow around the seeds by moving the displaced dirt back into the furrow.
An air seeder is commonly used in automated planting operations. The air seeder carries seed, fertilizer and possibly other chemicals in one or more reservoirs in communication with a pneumatic conveyance system. The pneumatic conveyance system uses air flow at such a velocity that the seeds and/or fertilizer are entrained into the air stream and are thereby conveyed through a seed tube or other tubes. Metering mechanisms control the flow of seed and fertilizer to the pneumatic conveyance system to control the rate of application of seed and fertilizer to the ground.
In a standard metering system, a fluted cylinder is provided, having valleys between raised ridges. Particles to be metered out from a reservoir are carried in the valleys as the cylinder rotates about a horizontal axis. The dimensions of the valleys are generally much larger than the size of the granules to be metered in order to ensure smooth operation. The valleys are generally spaced uniformly around the cylinder and along a length of the cylinder to distribute granules evenly from the granular distribution system (e.g., hopper). The metering cylinder can be a single unit or can be made of a horizontal stack of cylindrical elements. The number and size of valleys on a given metering cylinder determines the volume of granules metered per revolution of the cylinder. Where a low metering rate is desired, it is conventional to use a metering cylinder having smaller valleys to reduce the volume metered per revolution.
However, certain particles, such as metal granules used as micronutrient fertilizers, for example, are larger in size than the relatively small valleys of conventional “low rate” metering cylinders. If a larger size granule does not fit in a valley and therefore extends out of the valley, the large granule can contact the fixed surfaces of the metering mechanism against which the cylinder rotates. Such contact can damage the granule, potentially compromising the granule's effectiveness as seed, fertilizer, etc. If a large granule is too hard to crush, the cylinder will bind as it rotates, leading to excess torque load on the metering mechanism.
A metering cylinder with larger valleys uniformly spaced across the cylinder would allow granules to fit into the cylinder with room to move in response to contact with the fixed surfaces of the metering mechanism. However, use of a metering cylinder with larger valleys increases the volume metered per revolution, therefore not meeting a “low rate” per revolution requirement.
Accordingly, the present disclosure describes embodiments of an apparatus and method for metering seed or other particles from a hopper. The disclosed concepts are suitable for “low rate” metering of relatively large particles.